(a) Technical Field
The present invention relates to an apparatus and a method for controlling a humidification amount of a membrane humidifier for a fuel cell. More particularly, the present invention relates to an apparatus and a method for controlling a humidification amount of a membrane humidifier for a fuel cell, capable of controlling the humidification amount of the membrane humidifier relative to air supplied to a stack by adjusting a difference in partial pressure of moisture between the inside and the exterior of a hollow fiber membrane that constitutes the membrane humidifier.
(b) Background Art
In general, humidification of an electrolyte membrane in a fuel cell is required to operate a fuel cell system, and for this purpose, a humidifying apparatus is used which is operated in a manner in which humid gas discharged from the fuel cell exchanges moisture with dry gas supplied from outside gas.
Examples of the humidifying apparatus for the fuel cell include ultrasonic humidifiers, steam humidifiers, evaporative humidifiers, and the like, and as a humidifying apparatus used for the fuel cell, a membrane humidifier, which uses a hollow fiber membrane, is properly used. In particular, a configuration and an operation of a membrane humidifier for a fuel cell in the related art will be described below. The attached FIG. 1 illustrates an air supply system of a fuel cell system according to the related art, and FIG. 2 illustrates a membrane humidifier structure included in the air supply system in the related art.
The fuel cell system includes a fuel supply system configured to supply fuel (e.g., hydrogen) to a fuel cell stack, an air supply system configured to supply oxygen, which is an oxidizing agent required for an electrochemical reaction and contained in air, to the fuel cell stack, a heat and water management system configured to adjust an operating temperature of the fuel cell stack, and the fuel cell stack (hereinafter, referred to as a stack) configured to generate electrical energy using hydrogen and air.
Therefore, when hydrogen is supplied from the fuel supply system to a fuel electrode of the stack, and at the same time, oxygen is supplied from the air supply system to an air electrode of the fuel cell stack, an oxidation reaction of hydrogen is performed at the fuel electrode such that hydrogen ions (proton) and electrons are produced, and the produced hydrogen ions and electrons are moved to the air electrode via an electrolyte membrane and a separating plate, respectively, and water is produced at the air electrode through an electrochemical reaction among oxygen contained in air, the hydrogen ions and the electrons, which have been moved from the fuel electrode, and at the same time, electrical energy is generated from a flow of the electrons.
As illustrated in FIG. 1, the air supply system includes a membrane humidifier 100 and an air compressor 202 to supply humidified air (e.g., oxygen) to a stack 200. Therefore, exterior dry air is supplied into the hollow fiber membrane of the membrane humidifier 100 by a suction operation of the air compressor 202, and at the same time, discharge gas (e.g., humid air), which is discharged from the fuel cell stack 200 after the reaction, passes through the membrane humidifier 100, and in this case, moisture contained in the discharge gas permeates into the hollow fiber membrane to humidify dry air.
Referring to the attached FIG. 2, the membrane humidifier 100 in the related art includes a housing 101 having a supply port 102 formed at one end of the housing 101 and into which dry air flows from an air compressor, and a discharge port 103 formed at the other end of the housing 101 and from which humidified air is discharged.
A bundle of hollow fiber membranes, in which a plurality of hollow fiber membranes 106 are concentrated, are accommodated in the housing 101, and both ends of the bundle of hollow fiber membranes are accommodated by being potted (e.g., fixed) by typical potting members 108. An inlet 104 into which humid air discharged from the stack flows is formed in one circumferential portion of the housing 101, and an outlet 105 from which humid air from which moisture has been removed is discharged is formed in the other circumferential portion.
Therefore, when the discharge gas, which has been discharged from the stack after the reaction is completed, that is, the humid air is supplied from the inlet 104 of the housing 101 to the hollow fiber membranes 106, moisture is separated from the humid air by a capillary action in the respective hollow fiber membranes 106, and the separated moisture is condensed while passing through capillary tubes in the hollow fiber membranes 106, and then moved into the hollow fiber membranes 106. Further, the humid air from which moisture has been separated is moved along the exterior of the hollow fiber membranes 106, and then discharged through the outlet 105 of the housing 101.
Simultaneously, exterior gas (e.g., dry air) is supplied through the supply port 102 of the housing 101 by the operation of the air compressor, the dry air, which is supplied through the supply port 102, is moved through the hollow fiber membranes 106, and in this case, since the moisture separated from the humid air has been already moved into the hollow fiber membranes 106, the dry air is humidified by the moisture, and the humidified dry air is supplied to the air electrode of the stack through the discharge port 103.
Meanwhile, a humidification principle of the membrane humidifier will be described in more detail below with reference to the attached FIG. 3. When the humid air, which has been discharged from the stack after the reaction is completed, is supplied to an outer periphery of the hollow fiber membranes 106, and at the same time, dry air (e.g., exterior gas) supplied from the air compressor flows inside the hollow fiber membranes 106, water contained in the humid air humidifies the dry air in the hollow fiber membranes 106 while passing through the hollow fiber membranes 106, and the principle, that moisture in the humid air passes through the hollow fiber membranes 106, is achieved by transferring the moisture using, as a motive force, a difference in partial pressure of a fluid (moisture) between the inside and the exterior (indicated by {circle around (1)} and {circle around (2)} in FIG. 3) of the hollow fiber membranes 106.
Various methods are being researched to optimize performance in transferring moisture through the hollow fiber membrane of the membrane humidifier for the fuel cell. The above information disclosed in this section is merely for enhancement of understanding the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.